Research Excellence Attracts NIH Funding

Three new grants from the National Institutes of Health (NIH) support teams of Special Surgery surgeons and biomechanical engineers who are working to improve patient outcomes in joint and tissue replacement. At HSS, surgeons and engineers collaborate in the lab, where surgeons bring what they learn from their work with patients to the attention of biomechanical engineers.

Biomechanics at HSS

Biomechanical engineers see the musculoskeletal system as a machine designed to provide the body with movement and protect vital organs like the brain, heart, and lungs. HSS biomechanical engineers partner with clinicians to ensure that patients receive the implants they need to treat injuries and disease that have structurally altered their knees, elbows, and other joints. Faculty in the Department of Biomechanics at HSS collaborate with faculty in the Sibley School of Mechanical and Aerospace Engineering at Cornell University. The Cornell-HSS program has existed since 1978, creating strong ties between the institutions and fostering educational and research programs between engineering faculty and students in Ithaca, New York, and clinical and research staff at HSS.

Restoring Knee Function with Cartilage Implants

Biomechanical engineer Suzanne Maher, PhD, assistant scientist in the Tissue Engineering, Regeneration and Repair Program and a member of the Biomechanics Department at HSS, wants to identify the properties of an ideal meniscus replacement. The meniscus is a layer of cartilage that distributes forces across the knee joint. When the meniscus is injured, more force is borne by the remaining knee cartilage and the mechanics of the knee change. Eventually, knee osteoarthritis may develop.

HSS sports medicine surgeons, including Dr. Maher's co-investigator Surgeon-in-Chief Emeritus Russell Warren, MD, treat many patients who tear their meniscus through sports. Over 900,000 meniscus surgeries are performed each year in the United States, more than 3,500 at HSS alone. Currently, surgeons have three ways to treat meniscus tears: in a clean tear, the ends are sutured together; if the tear is not as clean, part of the meniscus is removed; and if the meniscus is damaged badly, it can be removed entirely and replaced with an allograft of healthy meniscus cartilage. In previous research, Drs. Maher and Warren and their team found that none of these methods fully restores the pre-injury mechanics of the knee. Even with surgery, increased pressure on knee cartilage persists, suggesting that patients suffering a meniscus injury may develop osteoarthritis at an early age, possibly requiring a knee replacement while still young.

Pioneering a Meniscus Implant

To improve outcomes for patients with meniscus injuries, Dr. Maher is developing a new solution: a synthetic meniscus implant to restore the knee's pre-injury mechanics and prevent early-onset osteoarthritis. As an initial step, Dr. Maher developed an experimental model to test how well the implants reproduce healthy knee mechanics. She developed the model by converting a knee simulator, a large machine that simulates knee movements during activities like climbing stairs that is usually used to test total knee replacements, into a machine in which she loads knees that have been inserted with her meniscus replacements.

The NIH is now funding Dr. Maher to validate her experimental model while simultaneously developing computational and statistical models that can be used by any scientist attempting to develop a meniscus implant to test the implant's effectiveness. Dr. Maher and her collaborators continue to develop their novel implant, which they test using their models.

"We are trying to make sure that the meniscal implant is doing mechanically what the surgeon wants it to do, which is to mimic the intact knee. This is how the surgeon will help the patient avoid early-onset osteoarthritis and restore quality of life," says Dr. Maher.

Making Implants that Last

Mathias Bostrom, MD, an HSS orthopedic surgeon specializing in hip and knee replacements, wants to improve the way bones heal and grow after joint replacement surgery, a process called osseointegration. The goal of Dr. Bostrom's research is to enhance bone growth into porous-coated joint replacement implants so that the implants will not loosen from the bone. Knee and hip replacements often remain successfully implanted for more than twenty years, and loosening is rare, but when loosening does occur, another (revision) surgery may become necessary.

Dr. Bostrom became interested in improving how bones and implants grow together as his clinical practice grew to include more revision surgeries, often repairing loosened joint replacements that were originally performed at other hospitals. He received an NIH grant in 2010 to support his decade-long collaboration with Cornell biomechanical engineer Marjolein van der Meulen, PhD. "At Special Surgery, there are clinicians like Dr. Bostrom who truly understand the importance of science, research, and biomechanics," says Dr. van der Meulen.

With the new grant, Drs. Bostrom and van der Meulen will explore ways to enhance bone ingrowth into prostheses. In the lab, surgeons work with engineers to stimulate bone growth into a porous surface by applying mechanical forces (also called loads), and by administering parathyroid hormone. "We want not only to optimize the body's own natural system of healing, but also to augment it with better materials to promote the healing process," says Dr. Bostrom.

Dr. Bostrom and his research fellows meet with Cornell engineers twice each week via video conferencing to discuss their ongoing research. The collaboration will provide information about whether patients should receive a bone growth hormone after surgery, and which porous surfaces are optimal for implants. It will also inform surgeons and physical therapists how much weight patients should put on their new joints post-operatively, and how soon. "I believe we'll see major strides in the area of osseointegration in the next few years that will help us get more people back to a pain-free life," Dr. Bostrom says.

Pioneering Modern Elbow Replacements

While elbow replacement surgery is less common than hip and knee replacement, HSS surgeons and engineers are working to make the procedure more successful for patients. In the past, innovation in elbow replacement has been limited, despite the devastating disability caused by the procedure’s relatively high failure rate. Now Timothy Wright, PhD, in collaboration with HSS orthopedic surgeons Robert Hotchkiss, MD, and Mark Figgie, MD, has been awarded the first ever NIH grant to improve the performance of elbow replacements.

HSS pioneered the modern knee replacement more than 30 years ago, and this research team is now pioneering the modern elbow replacement. "We hope to move elbow replacements to where hip and knee replacements are – so patients have a greater than 90% chance that they’ll still be fine after ten years," says Dr. Wright.

Because Drs. Figgie and Hotchkiss perform so many revision surgeries on patients whose initial elbow replacements fail (often repairing surgeries that were initially performed elsewhere), they wanted to discover why the failure rate for elbow replacements is so high. Suspecting that the problem was mechanical, they approached HSS biomechanical engineers Dr. Wright and Joseph Lipman, MS, and their Cornell collaborator, Donald Bartel, PhD. These five investigators began to meet weekly to analyze all aspects of failed elbow replacements, looking at patient charts, x-rays, and implants retrieved from patients whose implants had failed. They soon learned that the implants showed common signs of wear and loosening, which meant that they were not handling the mechanical forces, or loads, required of an elbow.

Analyzing Elbow Mechanics

Next, the team needed to know which forces were responsible for the damage they saw on failed implants. Working with the HSS Motion Analysis Laboratory, they recorded the movements of people with total elbow replacements as they performed activities of daily living. These motion patterns were then combined with a computer model to calculate the muscle forces responsible for creating these movements, which in turn could be used to calculate the loads directly across the elbow joint.

Using these preliminary findings of the mechanical failures sustained by elbow replacements and of the forces responsible for those failures, Dr. Wright and his colleagues secured NIH funding to continue their research. They will use the funds to expand the testing of elbow patients in the Motion Analysis Lab to create a more complete picture of the forces across the joint. They will then use those loads as inputs to computational and statistical models, similar in approach to Dr. Maher's in her meniscus implant, to design a novel elbow implant that will remain undamaged by the forces of the elbow muscles. :We’re designing a comprehensive system for replacing the elbow, one that facilitates treating patients with a broad range of elbow problems that require replacement to relieve pain and restore function," says Dr. Hotchkiss.

Dr. Figgie explains, "We want to give our patients a better elbow replacement that will restore function and provide the durability that we have achieved in total hip and knee replacement."

Collaboration that Works

While the ideas for all three of these studies emerged from the surgeons' clinical practices, the success of the ensuing research and development is due to the unique collaboration between surgeons and biomechanical engineers at Special Surgery. "Engineers provide clinicians with the mechanical background they need to solve clinical problems. The collaboration between surgeons and engineers is critical to the research we do at HSS, which is always aimed at improving outcomes for patients,” says Dr. Wright. "The NIH has confirmed its confidence in our unique approach to translational research by awarding these three new grants.”